1. Field of the Invention
The present invention is directed to the field of depth images and, more particularly, to a system that produces a lenticular image with improved viewing range and in which thickness of a lenticular faceplate or overlay applied directly to the image recording media is determined for the improved viewing range.
2. Description of the Related Art
Three-dimensional photography is comprehensively described in Three-Dimensional Imaging Techniques by Takanori Okoshi (New York: Academic Press, 1976, translated from the Japanese edition published in 1972) which provides a basis for describing the attributes and advantages of the present invention. Okoshi distinguishes between truly three-dimensional imaging and stereoscopic imaging. Integral photography is a method of recording a complete three dimensional spatial image, that is, one viewable from a multiplicity of directions, upon a single flat photographic plate. Integral photography refers to the composition of the overall image as an integration of a large number of small photograph image components. Each photographic image component is viewed through a separate small lens usually formed as a part of a mosaic of identical spherically-curved surfaces embossed or otherwise formed on the front surface of a plastic sheet. The plastic sheet is subsequently bonded to or held in close contact with the emulsion layer containing the photographic image components.
A lenticular photograph is a special case of an integral photograph where the small lenses have cylindrical refracting surfaces running the full extent of the print area in the vertical direction. The long cylindrical lenses are called lenticules, and the principles of integral photograph apply equally well to lenticular photography as long as one views the layouts or optical schematics in planes perpendicular to the cylindrical axis of the lenticule refracting surfaces. An optical method of making lenticular photographs is described by Okoshi in Chapter 4 of the aforementioned book. A photographic camera is affixed to a carriage on a slide rail and a series of pictures is taken in which the camera is translated between subsequent exposures in equal increments from a central perspective location to lateral perspective locations on either side of the central perspective location. The distance that the lateral perspective locations are displaced from the central perspective location is dependent upon the maximum angle through which the lenticular material can project photographic image components contained behind any given lenticule before it begins to project photographic image components of other portions of the image contained behind an adjacent lenticule. The sum of the total number of views contained between and including the extreme lateral perspective locations is limited by the resolution of the photographic emulsion which can be contained behind each lenticule and the optical characteristics of the lenticular faceplate.
In accordance with Okoshi, the negatives resulting from each of these views are then placed in an enlarger equipped with a lens of the same focal length as the camera lens. In making the print, an assemblage is made of a sheet of unexposed photographic material oriented with its emulsion side in intimate contact with the flat side of a lenticular faceplate, i.e., a clear plastic sheet having parallel cylindrical refracting surfaces embossed or otherwise formed into its front side. The assemblage is placed on the enlarger easel with the lenticular side facing the enlarger lens and the orientation of the cylindrical axes being adjusted normal to the direction of perspective shift in the views. The position of this assemblage on the easel is adjusted until the field of the central image is centered on the center of this assemblage, and an exposure of the information being projected out of the enlarger lens is made through the lenticules onto the photographic emulsion. Subsequently, negatives from the successive exposures are placed in the film gate and the position of this assemblage is readjusted on the easel in the same direction as the perspective shift in the views to reposition each respective view to the center of the assemblage, and additional exposures of the information being projected from the enlarger lens are made. When all the views contained between the lateral vantages have been exposed on the emulsion through the lenticular plastic sheet, the film sheet is separated from the lenticular plastic sheet-and developed. When the aperture of the enlarger lens is set to equal the amount of lateral shift between alternate views, the space behind each lenticule will be found to be exactly filled with photographic image components. The final step in this process is to again reassemble the developed photographic print media and the lenticular faceplate with intimate contact between the emulsion layer and the flat side of the faceplate, with the faceplate so positioned laterally that the long strips of adjacent images resulting from exposures through the cylindrical lenticules are again positioned in a similar manner under the lenticules for viewing. This method of image recording is called an "indirect" technique because the final print recording is indirectly derived from a series of two-dimensional image recordings. Because the exposure of the recording media is performed through the lenticular faceplate before the media is developed and attached to the faceplate, no consideration need be given to the thickness of the overlay material necessary for properly focussing the images toward the viewer.
Because the successive exposures in the prior art are performed in a fixed position with a restricted fixed field aperture, the image components align directly under the corresponding lenticules and the viewing range of prints created by this method is limited.
Ideally, an integral or lenticular photograph would display an infinite number of different angular views from each lenslet or lenticule to create an infinitely smooth viewing transition as is experienced in real life when viewing the world. This is practically impossible since each angular view much have a corresponding small finite area of exposed emulsion or other hard copy media which is its source of display. Consequently, as an upper limit, the number of views must not exceed the resolution limit of the hard copy media, and, perhaps practically more significantly, must not exceed the resolving power of the lenticules.
In addition to a lenticular faceplate, horizontal image separation may also be provided through raster occlusion, such as by using a Ronchi ruling on a faceplate spatially located in front of the composite print, so as to prevent the images intended for viewing by the right eye from being seen by the left eye and vice versa. The technique of raster occlusion is described in textbooks such as Foundations of the Stereoscopic Cinema by Lenny Lipton (New York: VanNostrand Reinhold, 1982, pages 74, 166, 287) and Stereoscopy by N. A. Valyus (Focal Press, 1966) and is the preferred embodiment of the International Patent Application publication number WO 90/08343 (Jul. 26, 1990) filed by D. J. Sandin, E. R. Sandor, W. T. Connally, and S. B. Meyers. Compared to lenticular methods, however, raster occlusion or barrier technology suffers from the additional problem of reduced image brightness. While the Sandin application mentions the use of a spacer with lenticulation on one side as a viewing device and is an "indirect" method, there is no discussion of or recognition of the conditions necessary to put this into practice.
U.S. Pat. Nos. 4,552,442 and 4,674,853, naming Graham S. B. Street as inventor, teach a "direct" method of recording images with correct angular correlation. In this method, the converging bundle of optical rays from a very large aperture camera lens is directed onto a sheet of lenticular material to which photographic film has been affixed in the same manner as described in the previously mentioned projection method. In optical terms, the apertures of the respective lenslets form the sub-apertures which sample the taking lens aperture. Left-right image correspondence is properly established by reflecting the converging beam from a beamsplitter onto a retroreflecting surface prior to reaching the lenticular assemblage. In the geometric space between the object field and the taking lens, different aperture coordinates, or positions on the aperture of the taking lens represent different perspectives of the object field. Bundles of light rays leaving the taking lens from localized sub-apertures within the taking lens aperture are relayed by different lenslets on the lenticular film array to the photographic emulsion optical reflections, and result in the need for a uniformly accurate retroreflector sheet with elements not substantially larger than the display print lenticules. Moreover, the depth of field of the camera lens severely limits the photographic space, and the camera itself is extremely large, necessitating the use of large format film sheets for each copy and a shutter means of very large aperture.
The Sandin application also illustrates a different technique for creating a three-dimensional image using a printer to electronically record the image on the recording media. However, no consideration is given to determining the proper spacer thickness for various printer scan line resolutions. As in the optical printing method, the image lines are restricted or limited to being aligned directly under the corresponding projection means.